Motor control system



T. E. Mc'DowELL 2,396,333

MOTOR` CONTROL SYSTEM l March 1.2, 1946.

Filed Jan. 1?-, 1944 Patented Mar. 12, 1946 UNITED STATES FATENT OFFICE.

MOTOR CONTROL SYSTEM Application January 17, 1944, Serial No. 518,493

6 Claims.

This invention relates to airplane landing eld locationing systems adapted particularly for enabling incoming air pilots to determine, just before reaching a landing field, the exact location of the eld when the runway, border and other lights on the field are invisible from above by being obscured by a comparatively low ceiling of smoke, fog, naze or the like. A system for this purpose is disclosed in my ecpending application Serial No. 409,705, nled September 5, 1941, now Patent Number 2,350,407, issued June 6, 1944. .In the system of this application light beam projectors or beacons are installed around the eld at some distance therefrom with the projectors operated by synchronous electric motors for synchronous oscillation of the beams in proper phase relation at predetermined intervals toward and away from the field, usually in vertical planes passing through the eld center.

An important object of the present invention is to provide simplified and improved control means for assuring synchronous operation of the motors and projectors and so that, in the event of failure of power supply to the motors, the motors and projectors will assume their proper predetermined phase relationship when the supply current llow is resumed.

A further object of the invention is to associate with each main or projector driving motor a synchronous pilot motor which runs continuously in synchronism with the power line frequency' and controls the current supply line to the main motor in such manner, that, after stoppage of the main motor due to current supply interruption, the main motor before being restarted Will be brought back into proper phase relation with the pilot motor and the other projector` operating motors of the system, when current supply is resumed.

Another object is to provide an arrangement in which the pilot synchronous motors are permanently directly connected with the main power line for continuously operating when the power line is in service, and to maintain operation of the pilot motors at synchronous speed, as by clock mechanism, when the main line power fails.

A further object is to provide an electric clock at each projector station connected with the power line and controlling a main switch for the supply line to the projector driving motory with the clock operable mechanically in case of power failure so that upon resumption of power supply the main switches at all of the projector stations may be opened or closed at the same time by the respective clocks. the clocks usually operating to hold the main switches open during the daytime and closing them for night service.

The above referred to and other features of my inventionl are embodied in the structure Figure 3 is an enlarged inner face view of av contact member driven by the pilot motor;

Figure 4 is a section 'on plane IV-IV of Figure 3;

Figure 5 is an enlarged inner face view of a contact member driven by the main motor; and

Figure 6 is a section on plane VI-VI of Figure 5.

Figure l shows a rectangular landing eld F having the longitudinally extending runways I0 and transversely extending runways II and also diagonal runways I2. Runway and border lights I3 are usually provided. I have shown four prolector or beaco-n stations A, B, C, and D located at some distance from the edge of the eld, probably a mile or two, depending upon the conditions of the terrain around the eld. Referring to Figure 2, at each station a beam projector frame VIl! is supported by trunnions I5 on a frame I6 which is usually mounted at the top of a tower I1, and within the frame I4 is the lamp I8 whose rays are to be projected. Extending from one of the trunnions of the frame I4 is a crank arm I9 connected by a connecting rod 20 with a motor M which may also be mountedv on the' Vment at the other stations being the same. A

service box Ellis provided for each station to which current is conducted through the line 22 from the power'line S. In the service box' are fuses 23, the current after flowing through the fuses being connected by the line 24 with a main switch 25. This switch is operated by a motor within an electric clock 26 which receives current through the conductors 2l. The clock may be of the well known type of astronomical time clock and may be set to open the switch 25 during the day time and close it for night service,

and the clock is adapted to operate mechanically' as by spring means wound up by a motor, so that the clock may function for proper control of the switch 25 in case of current failure from the power line.

The main switch 25 controls the connection with the power line S of the supply line 28 in which is the control switch 29 for the main motor M which drives the projector I4. The power circuit S may be of 110 volts, 60 cycle alternating current, but the lamp I8 in the projector need require only comparatively small voltage, and therefore this lamp is supplied with current from a transformer 30 in the line 3l extending to the lamp from the supply line 28.

The synchronous driving motor M has its shaft 32 connected with the crank shaft 33 through any suitable reduction gearing 34 for the desired rate of oscillation of the projector I4, the crank arm 35 on the crank shaft 33being connected vby the link 29 with the crank arm I9 of the projector.

Associated with the main motor M is the synchronous pilot motori? whose suppl-yline con nects through the lfuses 23 directlywith-the power line. A suitable reduction .gearing 371 VVis interposed `between the shaft vof lthe pilot motor and a shaft 38 on the outer end of which .is mounted a contact member 39. As bestshown in Figures 3 and 4, this member comprises a disk 4l) of `insulating material surrounded bye-,metallic contact or slip ring 4l .engaged vby a :brush A metal insert 43 -in vthe diskadjacent :to the slip ring is in electrical contact with the ring and may be integral therewith. This insert has the bore 44 therethrough in whichis mounted'a brush holder 45 for the brush 46, a spring 45' tending to urge the .brush outwardly.

The shafts of the motors MandP are-in axial alignment, and the shaft of -motor M drives a shaft 41 through a suitable reduction gearing 49, a contact member ,4 9being supported on the outer end of the shaft 41. Asbestshownin Figures 5 and 6, this contact member comprises Va.-dis k\ 5Il f insulating materalsurrounded 4bra .Contact or slip ring 5I. Afmetal insert l52 extends through the disk .5.0 which siir1.e1gutrca1 connection with the slip ring Y 1 and 4may .be integral therewith. The contact members39 and 49 yare,oppcsiteeach other I as shown on Figure 2, the insert-52 forming a contact for engagement -by the vbrush `46. The reduction gearings 3l and A4 8 are Asuch ythat when the motor'M is operating-the contact-member 4 9 will rotate at ,the same ,speed .as the ycontact member 3 9.

The control switch 29 for the motor M is controlled by an electro-magnetic device ,suchfas the solenoid ,54 whose core or armature is connected with the switch. One terminal of the solenoid winding is connected with one `side lof the motor supply line 2 8 and -its other terminal `is connected with the brush 53, the brush -42 b eing connected with the `other side of the supply .line 28. Upon current flow through the .solenoid winding, the Solenoid .Core will be moved tf1-@liet closure 0f the Switch 2S, and upon the fde-eeersization of the winding, a spring 45,5 will assist in returning the 001'@ for opening of -theswitoh' ,It is. very imptrtarlt that predetermined relative movements ofthe various .projectors be maine tend- .For example, ,it .may be ,desirable that the projectors simultaneously operate for down.- ward swing ofthe beams to be directed horizon.- tally towards 1the landing field and then to be swung back upwardly to vertical position. The function of the pilot motors is to maintain such synchronism and phase relationship of the projector operations. When the power line S .is on,

lli

the pilot motors will be continuously operating, but the supply circuits for the main motors may be interrupted, as when the main switches 25 are opened. The main motors might then move out of phase with each other, and if the motors were restarted from such .out of phase positions the projectors driven thereby would be out of phase. However, the pilot motors will function upon closure of the switches 25, to control the motor supply switches 29 for restarting of the motors M vin synchronism with the pilot motor, even though all the motors M do not Start at the same instant, so that the motors and the projectors would again operate in phase.

Referring to Figure 2, when the power line S is active, and thebrush 46 on the contact member 39 is in engagement with the contact 52 of the Contact member v.49, the circuit for the winding of the solenoid 54 will be closed for closure of the switch'29 for current supply to the motor M, the motor M then running insynchronism rwith the pilot motor. While these conditions are maintained at the various stations, the motors M will all be in phase with their pilot motors and the projectors will all be operated in power phase relationship. When the switches 25 are opened for day service by the .clocks 26 ,in the service boxes, and the supplylines 28 to the motors M are interrupted, the motors will stop, -but they may not Vall stop .in the-same position. Referring to Figure 2, upon interruption `of current flow through the `circuit 28, there will be no current flow through the solenoid circuit and switch .29 will be ,opened .and the .motor M will come to a stop, but the contact member .'39 would continue to be rotated by the pilotmotor to move its brush 46 .away from vthe contact 52 on thecontact member .49. If, when switch 2 5 is closed, which happens when the clock 26oprates fornight service, brush 4S is in engagement with-contact. 52, motor M will start immediately. However, .if brush 46 is notin .engagement with contact 52 when switch 25 is closed, motor `M will not start ,until .contact member 39 has carried .the brusharound .to catch up with contact .52 for ,closure of thesolen oid circuit and reclosure of switch 129, the motor M being then in phase with the pilot motor. This same control is ,effective at `all of the stations by the pilot motors and upon kclosure of the main switches .2,5 ,by ,the `clocks lat the stations, the timing of the connections of the motors back into service will lbe Vsuch that the motors and projectors will vcome into phase with each other and will maintain that phase .condition until the Vcurrent Vsupply is again interrupted.

It may require .a time interval for the motors to get back xto vfull speed and into phase with the pilot v motors after current supply .to .the motors has been reestablished, and therefore the contacts 52 of the contactmembers 49 are sufciently elongated for retention of contact with the brushes until the motors are fully up to Speed.

Although power failure Yfrom the power vline S is rare, there ,may be times when ysuch power failures will occur and it is therefore necessary that .the pilot .motors be kept running .at power line frequency so as to `be ready to function for control of the motors M when `.the main line power again comes on. The pilot .motor could therefore be constructed .to .operate like an electric synchronous Aclock which, Ywhen the power line current is on, would operate electrically to drive the reduction gearing 3l and the contact member 39, and during failure of power the v-reduction gearing and contact member would be driven mechanically by a spring which is wound up electrically when power is available. Synchronous motors of this type are available on the market and it is therefore unnecessary to show and describe the details herein.

The pilot motors can maintain a rate of revolution per minute different from that of the main motors, but the reduction gearings 31 and 48 must be such that the contact members 39 and 49 will always be driven at the same number of revolutions per minute when the motors M are in circuit. The revolutions per minute of the contact members could be the same as the number of oscillations per minute of the projectors by the motors M, or some even fraction thereof, as onehalf, one-third, one-fourth, etc. For example, the pilot motors could run at 8600 revolutions per minute and the main motors at 1800 revolutions per minute, with the rate of oscillation of the projections 20 revolutions per minute, and the Contact members 39 and 49 operating at 20 revolutions per minute. Or, with the pilot motors running at 3600 revolutions per minute and the motors M at 1800 revolutions per minute, the reduction gearings 3l and 48 could be set for rotation of the contact members at 10 revolutions per minute, with the projectors being oscillated at the rate of 2O revolutions per minute.

With my improved control, irrespective of the positions of the contacts 52 relative to the brushes 4E at the time of stopping of the motors M, the pilot motors will function, upon resumption of current supply to time the restarting of the motors M for operation thereof in phase with the pilot motors and operation of the projectors in proper phase relationship. With the clocks 26 in the service boxes operable electrically when the power line is functioning, and mechanically when the power line fails, the main switches 25 at the various stations will be simultaneously controlled for opening or closure at predetermined intervals.

It is evident lthat my improved control means may be used in other systems where devices are to be operated in desired phase relationship by synchronous motors. Changes or modifications may also be made in the control Larrangement shown and described without departing from the scope of the invention.

I claim:

1. In a system in which a number of devices are each operated by a synchronous driving motor supplied from an alternating current power line, control means for maintaining operation of the motors and the driven devices in predetermined phase relationship, said control means comprising a continuously running synchronous pilot motor associated with each of the driving motors, a current supply circuit for each driving motor, and control means for said circuit conjointly controlled by the driving motor and the associated pilot motor in such manner that upon opening of the supply circuit and stoppage of the driving motor the circuit will not be reclosed for restarting of the motor until the pilot motor comes into phase with the driving motor whereby upon restarting of the driving motor the device driven thereby will be in phase with the other devices of the system.

2. In control systems in which a number of devices are operated b-y synchronous driving inotors connected with an alternating current power supply line, control means for said driving motors for insuring operation of the devices at all times in predetermined phase relationship, said control means comprising a synchronous pilot motor associated with each driving motor and running continually in synchronism and phase with the frequency of the power line, a supply circuit for connecting each driving motor with the power line, a control switch for opening and closing said supply circuit, electro-magnetic means for operating said switch, a control circuit for said electro-magnetic means, and control means for said electro-magnetic circuit means conjointly controlled by said driving motor and the pilot motor associated therewith in such manner that said switch will be closed when the driving motor is in phase with the pilot motor but will be opened when the driving motor is out of phase with the pilot motor.

3. In combination, a synchronous driving motor, a current supply circuit for connecting said motor with an alternating current power line, a switch in said supply circuit, electro-magnetic means for operating said switch, a circuit for said electro-magnetic means connected to receive current from said supply circuit in advance of said switch, a synchronous pilot motor permanently connected with the power line, a pair of contact members forming terminals for said electro-magnetic means circuit, one o-f said contact members being continuously rotatable with said pilot motor, the other contact member being rotatable by said driving motor at the same speed as the pilot motor contact when said driving motor is operating, said contact members being free of mechanical interconnection and being in electrical engagement only when said driving motor is in phase with said pilot motor whereby said electromagnet means circuit will be energized for closure of said switch and current ow to the driving motor, stopping of said driving motor upon failure of flow from said power line to said supply line causing said contact members to become disengaged and vsaid electro-magnet means circuit opened for opening of said switch, said switch after resumption of flow from the power line to the supply line being reclosed only after the contact member rotated by the continuously operating pilot motor is reconnected with the contact rotated by the driving motor and the vdriving motor is in phase with the pilot motor.

4. In a system in which a number of devices are to be operated by synchronous motors in predetermined phase relationship, control means for maintaining such phase relationship comprising a continuously running synchronous pilot motor associated with each driving motor, a current supply circuit for each driving motor, and contact members movable with the driving motor and pilot motor respectively for effecting closing of the supply circuit only when the driving motor is in phase with the pilot motor whereby the driving motors can be started after a period of stoppage thereof only after being brought into phase with their respective pilot motors and whereby the devices operated by said motors will be maintained in proper phase relationship.

5. In a system in which a number of devices are operated by synchronous motors in predetermined phase relationship, control means for maintaining such phase relationship comprising a synchronous pilot motor associated with each driving motor, the pilot motors being permanently connected with an alternating current power line to run continuously in synchronism and phase with each other, a supply circuit for each driving motor, a main switch controlling the connection of said supply circuit with the power line, a secondiswitchcontrolling.the connection of the suppl'ynicircuit 'with Jthe drivingr` motor, electro-niagneticcontrol-'means fo'rsai'dfsecond' switch having an "energizing circuit, a contact driven by the pilot'moto'rat reduced speed througha circular path, aVv contact driven by the driving motor at reducedlspeed through a circular path,lsaid contacts yloeingdriven at the'same Yspeed when the driving motor is in synchronism with thepilot motor, said contacts being free of mechanicaLinterconnection and'l'ormingthe terminals of said electro-magnetic control means circuit, said ener- `gizing circuit, after closure of said main switch, being closedforclosure of said second switch by said'electroniagnetic control means only when the pilot motor driven contact comes into engagement with-thedriving motor driven contact and the 'drivngmotor is in phase with'thelpilot motor, wherebylclosure of the main switchesin the system after-'opening thereof 'will result in starting of all the driving motors in phase with each other and withthedevices operated bythe driving motors in their proper phase relationship.

6. `Ina system in which'a number of devices aref to be operated by synchronous motors in predetermined phase relationship 'i and in l which ia supply line Vis l provided ifor 'each driving .motor for connecti'nglitlwith a power line, control means for assuringrestarting of said drivng'motors and the devices operated'thereby in proper-phase relationship upon resumption of power after a power failure, said contro-l means comprising a synchronous pilot motor associated with each driving motor, -said pilot motors being permanently connected with the power line to be continuously electrically operated in synchronism and phase' relationship with each othell when the power ison; and adapted to mechanicallyfrnantain such operationupon power failure, a switch in the, supply line foreach driving motor, means automatically opening saidrswitches upon power failure, `and Vmeans jointly controlled -by `each driving motor` and its associated pilot motor to he erective upon power return to reclose the-supplycircuit switch for restarting of the driving motor only when the pilot motor Vcomesl into phase with the driving motor,

THOMAS NICDOWELL. 

